Date of Graduation

1-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Space & Planetary Sciences (PhD)

Degree Level

Graduate

Department

Space & Planetary Sciences

Advisor/Mentor

Vincent Chevrier

Committee Member

Larry Roe

Second Committee Member

Timothy Kral

Third Committee Member

Colin Heyes

Keywords

Co-crystals, Evaporites, Experimental Techniques, FTIR Spectroscopy, Organic ices, Planetology, Titan

Abstract

Titan is the only other planetary body in the solar system with liquid on the surface. With a surface temperature and pressure of 89 – 94 K and 1.5 bar (N2), respectively, Titan’s lakes are comprised of liquid hydrocarbons, predominantly methane and ethane. Over time, Titan’s lakes may evaporate, leaving behind residual deposits (evaporites). The evaporation processes and composition of the evaporites is poorly understood. I address these outstanding questions by experimentally investigating the physical and spectral properties of evaporites at Titan surface conditions using an experimental chamber.

Chapter 1 addresses the formation of ethylene evaporites. Ethylene evaporites form more quickly with pure methane, because methane readily evaporates at Titan surface conditions. Ethylene absorption bands at 1.630 and 2.121 μm are redshifted after evaporite formation. These results imply that ethylene is a good candidate for Titan’s evaporites, although they may be restricted to methane-dominated lakes/seas.

Chapter 2 addresses the ability to detect the formation of the acetylene-benzene co-crystal using FTIR spectroscopy. The co-crystal is easily identifiable upon formation at ~135 K, as evidenced by drastic spectral band shifts, several new bands in the C-H stretching and combination bands regions, and clear morphological changes of the sample. The co-crystal is stable down to Titan temperatures (90 K). Studying co-crystal formation provides insights into co-condensation in Titan’s atmosphere, and evaporite formation and composition.

Chapter 3 investigates the formation of evaporites with acetonitrile. Acetylene and acetonitrile form a co-crystal between 118 – 174 K, which is stable down to 90 K. New bands at 1.676 µm and morphological changes to the sample confirm co-crystal formation. We observe new shapes to NIR absorptions that were not previously present in pure component experiments. These results have implications for astrobiologically relevant co-crystals and where nitrile compounds may accumulate on Titan.

Chapter 4 addresses more complex evaporite experiments (“binary” experiments) with two evaporite molecules combined. Acetylene is the most prominent species in these experiments, and the acetylene-acetonitrile co-crystal is stable before, during, and after methane evaporation. These results and future binary experiments can help assess the validity of evaporite models, and represent a more realistic view of evaporite solutions.

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